We studied median somatosensory evoked potentials (SEPs) in an unselected series of 30 patients with sporadic motor neuron disease (MND). SEPs were affected in 17 patients (57%), with a higher incidence of abnormality in amyotrophic lateral sclerosis and bulbar palsy than in progressive muscular atrophy. In a majority of patients, simultaneous bilateral stimulation of the median nerve revealed a delay or absence of scalp-recorded central N32 and/or N60, leaving the earlier peaks intact. In the remaining cases, the N19 peak was asymmetrically prolonged. These findings suggest common involvement of somatosensory pathways in MND, either at cortical or subcortical levels, and correlate with neuropathologic reports of neuronal degeneration beyond the primary motor system.